London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

A leading food expert has warned that the Government cannot be sure that there is no risk to public health from beefburgers contaminated with horse DNA.

Dr Duncan Campbell, former president of the Association of Public Analysts, told the Guardian newspaper it was a "reflex" by the Food Standards Agency (FSA) to say there was no safety aspect to scandals of this type.

Dr Campbell said: "All we know is it is not a beefburger. What is it? We don't know. Why was it picked up in Ireland and not the UK, and how long has it been going on? Until we know what the source is of the 'horse' or 'something derived from horse', we cannot be sure there is no food safety risk."

Dr Campbell said there could also be a risk from medicines used for animals that were not sanctioned as safe for the human food chain, and questioned whether raw food materials could be coming from slaughterhouses that were not approved for processing meat for human consumption.

Dr Campbell, the chief public analyst for West Yorkshire, is a leading expert on meat quality and will be part of the official investigation into the horse meat scandal, the Guardian said.

More than 10 million burgers have been taken off supermarket shelves across Ireland and the UK after horse meat was discovered in burgers sold by Tesco, Aldi, Lidl and Iceland. Aldi, Lidl and Iceland also withdrew burgers from sale after they were found to contain horse meat.

Sainsbury's, Asda and the Co-op later withdrew some frozen products but stressed that the move was "purely precautionary" and they had not been found to be selling contaminated food.

On Friday farming leaders called for immediate action by supermarkets to improve their sourcing and labelling of food. NFU president Peter Kendall said the integrity of UK-produced meat was being compromised by the use of cheaper imports which did not meet the same stringent monitoring systems.

The Food Safety Authority of Ireland (FSAI) stood by its position that there was no risk to public health from the presence of horse or pig DNA in beefburgers, the Guardian said, and any bacterial contamination would be killed by cooking.

It also said it had said it had found no race of phenylbutazone, a horse medicine not allowed in the food chain.